Purification of thiophenols by treatment with aluminum



'" itd 1 tiara Patented Oct. 18, 1960 PURIFICATION OF THIDPHENOLS BYTREAT- MENT WITH ALUMINUM Donald C. Jones and Robert J1 Earlier,Pittsburgh, Pa, assignors to Consolidation'fioal'Company, Pittsburgh,Pa;, acorporationof'Pennsylvania N Drawing. Filed Nov. 23,1959,- Ser.No. 854,543

7 ciarims; oi; air-soar This invention relates to the art of separatingthiophenols from tar acids. More particularly it relates to purifyingthiophenols' contaminated with tar" acids by selective reaction of'tlie'tar acids with aluminum to form aluminum salts.

This application" is a continuation-impart of our" copending applicationSerial No. 807,278, filed April 20, 1959, now abandonedi By tar acidsreference'is' made to those constituents present in coal-tardistillates, certain cracked petroleum distillates and the like, often"referred to collectively as phenols, which are soluble in" dilutecaustic soda, giving sodium cresylate. We particularly refer to amixture of the simpler mono'hydric phenols'boiling below about 230 C.and consistingalmost' entirely of a mixture of phenol,- rnethylpheriols('cresolS) and dimethyh phenols (xylenols), with lesser amountsoccasionally present of ethylp'henols and'tiimetliylplien ols. I I

By thiophenols refern eis made to the "a'r'yl mercaptans. Ofparticularcommercial 'interest'isthiophenol per se and the lowermolecular Weight alkylthiophe'nols, such as the thiocresols"andthioxylenols.

At present; thiopheiiols areprincipally obtained from two sources; as aby productfroir'i'the caustic extraction of petroleum distillatesand'b'ys'ynthetic methods starting with benzene. In onewidel'yused'direct synthesis tech nique, the benzene is converted tobenzenesulfonylchloride by treatmenfwitha molar excessofchlorosulfonicacid. The product isth'e'n' converted to thiophenol by reduction inthe"p'r'eseiice' of aniet'al-ac'id system: While the resulting'product'is of'li'igh purity andparticularly useful for paint, dyestuifs' andpharmaceutical applica tions, it is relatively expensive. This preventsitswidespread use for niany'applications.

In obtaining thiophenols from petroleumdistillatesresulting from oilcrackin'g' processes, the tar acids and thiophenols are recovered by"extracting the petroleum distillate with aqueous ca'ustic'solu'tion' toproduce watersoluble tar' a'cid'salts". Inthis"processof'extraction;thio= phenols present are" also removed by the aqueous caustic solutioninasmuch as the thiophenols' areeven' stronger acids than' the phenolsor tar acids themselves; The quantity of thiophenols in theoriginalsource material varies widely, being sometimes as little as'one percentby weight of the phenols and ranging as high'as25'p'ercent and above.The thioph'enolsfound inthe caustic extract consist principally ofthiophenol' itself and'mixecl thiocresols and thioxylenols.

In US. Patent'2',767,220, a process is setfortlifor'p'urifyingthiophenol-contaminatedtar acids that are substantially free of neutralhydrocarbon oils. In this process, the feedstock,consistingprincipallyof tar acids and thiophenols, is contacted withaqueousmethanoland'with'a low boiling parafi'lnic naphtha fraction in acontinuous countercurrent extraction zone. The aqueous methanolsolutiondissolves substantially all the tar acids, and the naphthafractiondissolves the thiophenols. The naphtha fraction" is'distilled'ed to yield the thi'ophen'ols as still bottoms. Inasmuch as thepurification of the tar acids is the desideratum of this process, thethiophenols recovered from the paraffinic naphtha fraction invariablycontain from 2 to 20 percent tar acids by weight. Complete removal ofthe tar acids from the thiophenols does not take place even when thethiophenols are fractionally distilled in a highly efiicient column,such-as a 50-plate packed tower. Thiophenol from such a distillationcontains approximately 1.5 percent phenol. Eflicient fractionaldistillation is likewise unsuccessful ineffecting a significant removalof the tar acids from the mixed thiocresols and thioxylenols. Thesethiophenols contain even higher amounts of close-boiling tar acids.

It is accordingly an object of the present invention to provide athiophenol of improved purity with respect to tar acid content.

It is a further object to provide a method for obtaining thiophenolsfree from tar acids that is readily adaptable to existing techniques forextracting tar acids from petroleum distillate fractions.

The process of the present invention provides a thiophenol of improvedpurity with respect to tar acid content. lt further provides a methodfor enriching a mixture of thiocresols with respect to o-thiocresolcontent.

In accordance with this invention, a mixture containing thiophenols andtar acids is reactedwith aluminum, preferably in finely divided form, ata temperature at which the tar acids present selectively react toformaluminum phenoxides. The thiophenols are then separated from therelatively nonvolatile aluminum p'henoxide, preferably by distillation.It is particularly preferred, andfor certain purposes essential becauseof process operability and product purity requirements, that thealuminum used be aluminum metal per se free from activators orpromoters, such as inorganic mercury salts, which are used to stimulateor enhance its reactivity;

Commercially available finely divided aluminum foil of 99+ percentpurity is preferred for. use in'practicing' this invention. This finelydivided aluminum foil in approximately A-inch squares is ordinarilyusedas a pigment in aluminum paint. It has a protective film of. acutting oil which prevents'oxidation of'the aluminum without interferingwith the purification of the thiophenols- While aluminum in granularform or aslathe turnings is also suitable, the reaction is generallyslower, presumably because of the reduced surface available comparedwith the aluminum foil.

It has been found that this method is suitable for rendering anindividual thiophenol'or mixtures of thiophenols containing tar acids inamounts up to 50 percent by weight substantially free from tar acidcontamination.

The method is particularly preferred where the thiophenol has a tar acidcontent of up to 20 percent by weight of the mixture. In general, wherethiophenol itself'is to be purified, the contaminant present is usuallyphenol. 7 It is believed that an azeotrope is formed thereby preventinga separation of the thiophenol and phenol by conventional distillationtechniques. Alkylthiophenols are generally contaminated by correspondingalkylphenols. Thus mixed thiocresols are usually contaminated witho-cresol, o-ethylphenol and other tar acids. The thioxylenols generallycontain contaminating amounts of close-boiling cresols and xylenols. forpurifying tar acid-contaminated thiophenol and lower alkylthiophenolssuch as thiocresols and thioxylenols.

As a preferred method of practicing this invention, the thiophenolcontaining a minor portion of tar acid'is conveniently charged to abatch still along with at least one third of a gram atom of aluminumfoil per gram mole of tar acids present in the charge. Additionalaluminum is required to reactwith any moisture present. An excess Thisprocess is particularly useful of aluminum above the stoichiometricamount is ordinarily not required for substantially complete removal ofthe tar acids if moisture is not present. Excess aluminum, dependingupon the reaction temperature and specific thiophenol, may react withthe thiophenols, thereby lowering their yield. The charge is heated atatmospheric pressure to a temperature between 100 and 220 C., dependingon the thiophenol and the phenolic contaminant present. The lowermolecular weight phenols and thiophenols react at the lowertemperatures.

A preferred reaction temperature range for a thiophenol-phenol mixturein which evolution of hydrogen at a satisfactory rate occurs with thealuminum is between 135 and 170 C. For mixed thiocresols, a rangebetween 140 and 185 C. is preferred. The mixed thioxylenols have apreferred reaction range between 160 and 200 C. Where the purifiedthiophenol is subsequently distilled off at atmospheric pressure, apreferred upper limit for the reaction temperature range is the refluxtemperature of the thiophenol being purified. Where substantial amountsof tar acids are present, in excess of 20 per cent by weight, asatisfactory rate of evolution of hydrogen occurs at the lower end ofthe range or even at lower temperatures. The evolution of hydrogen isusually com.- pleted within 5 to 30 minutes depending on the rate atwhich the pot temperature rises. The reaction with aluminum isexothermic. Therefore, in a situation requiring rather large amounts 0.5percent) of aluminum, the reaction, once initiated, may boost thetemperature by 20 C. or more, thus speeding the reaction rateconsiderably. When the vigorous evolution of hydrogen has ceased, thepressure is then reduced and the purified thiophenols are recovered asan overhead distillate. The residue contains the aluminum salts of taracids and may also contain some aluminum salts of the thiophenols,depending on reaction conditions and on the excess quantity of aluminumemployed. The residue may be hydrolyzed by aqueous acid such as dilutehydrochloric acid and the organic materials recovered if desired.

This process is particularly applicable to the purification of mixturesof thiophenols and tar acids as recovered from the paraffinic naphthafraction obtained from the double-solvent extraction method of treatingcaustic-extracted petroleum distillates, as set forth in US. Patent2,767,220. However, the process is also applicable to refiningthiophenols contaminated with other substances in addition to tar acidsin that these other contaminants are removed by fractionation eitherbefore or after treatment of the thiophenol with aluminum.

The procms is also considered applicable to the removal of trace amountsof moisture and alcohols, as well as phenols, from aromatic thiols,i.e., thiophenols. Excessive amounts of moisture, however, particularlyWhere non-amalgamated aluminum is used, require too long an inductionperiod for reaction to commence. It has been found that, in general,aluminum becomes selectively less reactive in going from water tophenols, to alcohols to thiophenols. Thus an equilibrium involvingAl(OR) and Al(SAr) should very strongly favor the former. Distillationwould not affect the equilibrium position significantly if the alcoholinvolved were of a similar volatility to the thiophenol; if the lattersituation were not involved, then the separation would, in any event,ordinarily be carried out by distillation.

Somewhat surprising is the finding that magnesium cannot be used topractice this invention, despite reports in the literature of theformation of magnesium phenoxides. The reaction proceeds verysatisfactorily with aluminum, which is preferably in granular, flake orfoil form. For granular aluminum, a 20- to 30-mesh U.S. standard sievesize is suitable. Finely divided aluminum foil or flake is particularlypreferred.

As will be hereinafter described, it has been found that the use ofaluminum amalgam or aluminum added oo- 4 jointly with an inorganicmercury salt such as mercuric chloride greatly accelerates the rate ofreaction, which generally may be conducted at lower temperatures,compared with use of aluminum alone. However, for many applications,problems of mercury contamination are of consequence, and the use ofaluminum amalgam must be avoided. Thus the use of aluminum that has notbeen treated with a mercury salt avoids difliculties frequentlyencountered when mercuric chloride that is initially present is reducedto mercury metal and, during distillation of the thiophenol, carriedover in the overhead distillate. Thereby the thiophenol is contaminated,and the distillation column may also require to be cleaned. Thus it hasbeen found that in such a reaction system although the use ofaluminum-mercuric chloride leads to a more vigorous reaction, entrainedmercury generally appears in the overhead distillate. Unless highlyeflicient fractionating columns are used where the distillate fractionsare taken off at a high reflux ratio, the obtaining of mercury-freedistillate is difficult. Distillation at lower reflux ratios frequentlyresults in a cloudy distillate being obtained, the resulting sedimenteventually coalescing to mercury. Thus for most commercial applications,the use of aluminum amalgam or aluminum-mercuric chloride is to beavoided in order to eliminate the necessity for frequent column cleanupand also to eliminate requirements for redistillation of the distillatefractions obtained in order to render them free from mercury.

In addition to the freedom from contamination obtained by using aluminummetal without a mercury salt activator such as mercuric chloride, otheradvantages are also present. Eliminating use of a mercury salt obviouslypermits a cost saving. In addition, the reaction of aluminum metal alonewith a mixture of thiophenols and tar acids at well below theatmospheric boiling point of the mixture is highly selective becausealuminum is essentially unreactive with respect to thiophenol except atelevated temperatures. In the usual situation, in which the tar acid isa minor component, the reaction with essentially pure aluminum of 20-30mesh granular size, or even in foil form, proceeds quite slowly comparedwith the reaction rate when an aluminum amalgam or aluminum mercuricchloride combination is used.

When the rate of gas evolution has diminished greatly relative to itsmaximum value, the pressure may be reduced and the purified thiophenolsreadily recovered by distillation. Further, the slower reaction rateoccurring with aluminum alone permits charging all of the alumi nummetal to the still pot simultaneously with the thiophenols. In the eventthat the charge contains relatively small or trace amounts of moisture,no hydrogen evolution will ordinarily occur until an overhead distillatefore-cut has been removed. Thus it may not be necessary to completelydry the thiophenols prior to the addition of the aluminum, whererelatively small amounts of moisture are present, provided a sufficientexcess of aluminum is used to first react with the moisture present.

It the reaction mixture is cooled to room temperature or lower, agelatinous precipitate of aluminum phenoxides is formed. This may thenbe partially separated from the thiophenols by filtration orcentrifugation. However, it is ordinarily preferred to separate thethiophenols from the relatively nonvolatile aluminum phenoxides bydistilling off the thiophenols from the mixture without any priorcooling of the mixture.

The following examples illustrate this invention but are not intended aslimitations thereof.

EXAMPLE 1 Reaction of aluminum with thiophenol-phenol mixture A504.4-gram sample of thiophenol containing 1.8 percent by weight phenolwas reacted with 5.0 grams (a 456% excess) of 20-30 mesh granularaluminum at the atmospheric reflux temperature. Reaction commenced 5after a small amount of moisture had been removed in a distillatefore-cut. Hydrogen evolution practically ceased after 2.5 hours, eventhough a considerable amount of aluminum remained unreacted. Thepressure was then gradually reduced and an 87% recovery of phenol-freethiophenol was obtained.

EXAMPLE 2 Reaction of aluminum with thiocresol-o-cresol mixtureTreatment of 500 grams of mixed thiocresols containing 24.5 grams (0.227mole) of o-cresol with 4.15 grams of 20-30 mesh granular aluminum (a100% excess) at a reflux temperature'of 192194 for 0.2 hour yielded 140%of the theoretical hydrogen which would be formed by complete reactionof the o-cresol present. The pressure was then reduced, and an 88%recovery of o-cresol-free thiocresols was obtained.

EXAMPLE 3 Reaction of aluminum with thiophenol-tar acid mixtureApproximately /3 of a gram atom of aluminum in the form of shreddedaluminum foil per gram mole of phenol plus o-cresol present was reactedwith the thiophenol-tar acid mixture by refluxing at 169170 C. at oneatmosphere in a 1" x 3' Vigreaux column. About 4 to 5 hours was requiredfor completion of the reaction. The thiophenol was distilled overheaduntil boilup fell off and pot temperature started to increase rapidly.The thiophenol distillate was found to contain no phenol or o-cresol asdetermined by gas chromatographic analysis.

EXAMPLE 4 Purification of xylenol-containing thioxylenols A-commerciallyobtained thioxylenol sample was reacted with excess aluminum flake at atemperature between 190 and 210 C. for 4 hours. The excess amount ofaluminum used in two different runs represents the excess over thestoichiometric requirements for reacting with the tar acids present inthe thioxylenols. After cessation of gas evolution, the reaction mixturewas cooled and decanted. The decanted phase was fractionated through apacked column, and a heart-cut distillate, boiling 12l125.5 C./50 mm.Hg, corresponding to 91 weight percent of the still charge, wasobtained. Analysis by gas chromatography showed the thioxylenols to besubstantially free of tar acids. The results obtained were as follows(in weight percent):

100% excess Aluminum 150% excess Aluminum Feed Neutral oil m-p-Cres olsThiocresols 2,4-2,5-Xylenls Thioxylenols Trace Trace 0. 4 0. 4 0. 3. 6Trace 0. 96. 0 99. 6 99.

Trace Trace EXAMPLE (a) Removal of neutral 0ils.-Crude thiophenol, 67pounds, which contained about 6% neutral hydrocarbon oils, 7.5% phenoland some o-cresol was charged to an evacuated kettle and blanketed withnitrogen. Then 120 pounds of 20 weight percent sodium hydroxide wasadded, which resulted in an increase in kettle temperature from 11to'40" C. After stirring, an additional 25 pounds of water was added.With the overhead system set up for total take-off, the kettle washeated and neutral hydrocarbon oils and water were distilled off at a 95C. head temperature and at atmospheric pressure. The first materialrecovered overhead consisted of 52 weight'percent water and 48 percentneutral oil. At a boil-up rate of 13-14 liters per hour, all the neutraloil which could be recovered came over within one hour. Of the 27.8pounds of total overhead product, 2.8 pounds was neutral oil. Anadditional 20.4 pounds of water was then taken overhead.

The'material remaining in the kettle was cooled to 50 C., and pounds of40% sulfuric acid was added in 10-pound portions with stirring. Thetemperature rose to 64 C. during this operation, thereby requiringcooling of the kettle under a nitrogen blanket to a temperature of 50 C.Inspection of the lower (aqueous) phase revealed that it was still basic(pH of 8) so that a small additional amount of sulfuric acid was addedand stirred in. This was suflicient to render the aqueous phase acidic.It was then withdrawn (183 pounds), and 2.5 pounds of 10 weight percentsodium hydroxide was stirred in. After a bottom basic phase of 2 poundswas recovered, 4 pounds of water was stirred in and the kettle contentswere then drained. The lower organic phase weighed 62 pounds, and theaqueous top phase weighed 6 pounds. This procedure was also repeated fora second batch so that 117.5 pounds of substantially neutral oil-freethiophenol containing phenol and o-cresol was available. The 117.5pounds of thiophenol (lower organic phase) Was recharged to the kettleand dried by distilling off water present together with low-boilingcontaminants at 150 mm. Hg pressure to a head temperature of C. The 6.2pounds of material recovered overhead was mostly thiophenol (dark).

(b) Reaction with aluminum.After the kettle was cooled to 78 C., 1.8pounds of flake aluminum was added, and heating was resumed. At 158 C.the reaction became sufficiently exothermic so that the heat input wasreduced temporarily. Evolution of hydrogen continued for about 1% hours,the hydrogen being diluted with nitrogen in the vent line before it wasreleased to the atmosphere. During the aluminum phenoxide formation, 5.5pounds of thiophenol (dark) was distilled off and/ or entrainedoverhead.

The kettle temperature was then raised slowly and the thiophenol wastaken overhead. Approximately 90 pounds of thiophenol (clear,water-white) was recovered at a head temperature of 161 C. with amaximum pot temperature of 188 C. The kettle was then cooled preparatoryto placing the system under vacuum, and the receiver was drained.Another 4.6 pounds of thiophenol (dark) was then recovered at about 75mm. Hg pressure. The kettle was finally cooled to permit the addition oftar acids to render the residue less viscous for withdrawal.

The starting thiophenol for reaction with aluminum containedapproximately 92% thiophenol, 8% phenol and o-cresol, after it had beenfreed from substantially all of the neutral oil. The analysis of thefinal product was: 0.4% neutral oil, 98.4% thiophenol, and 1.2% mixedthiocresols. No phenols could be detected. The yield of pure thiophenolobtained is approximately 67% based on the initial crude thiophenolstarting mixture, and 90% based on the actual thiophenol content of thecrude mixture.

EXAMPLE 6 Large-scale purification of phenol-contaminated thiophenol A125-gallon reaction kettle was charged with approximately 1.5 drums (621totalpounds) of a thiophenol mixture containing 96.4% thiophenol, 2.74%phenol and 0.86% neutral oil. Because of the deleterious elfect of wateron the aluminum catalyst, residual water present in the distillationunit was first removed. To accomplish this, vacuum was applied (1l5 mm.Hg pressure) followed by steam heat, and the kettle contents and systemwere dehydrated to an overhead vapor temperature of 97 C. The heat wasthen turned oif and'the 7 vacuum was released with nitrogen purging. Thedis.- tillate, weighing 67 pounds, contained approximately 85% water,14% thiophenol, 0.4% phenol and 0.1% neutral oil. The dehydrationresidue weighing 611 pounds, contained 96% thiophenol, 3% phenol, and 1%neutral oil. 2.13 pounds of flake aluminum was then added to the residue(2.13 pounds; 0.35% of the total weight of the charge, 33%stoichiometric excess). The total time to this point was 100 minutes.

Heat was again applied, and after 95 minutes the kettle contents reacheda temperature of 157 C., at which point the aluminum reaction becamequite vigorous. The temperature in the kettle was maintained at 155160C. for a period of two hours. The kettle was then cooled to 70 C. andthe reaction residue transferred under vacuum to the distillation unit.The distillation was carried out at a pressure of 70 mm. Hg and wascompleted in 3 hours. All overhead material was clear and light incolor. The final distillate product weighed 490 pounds and analyzed as99.1% thiophenol and 0.9% neutral oil. No phenol whatsoever could bedetected in the distillate. The residue contained thiophenol, neutraloil, aluminum phenoxide and aluminum thiophenoxide. The recovery of thethiophenol, based on the initial charge, amounted to 96.3%. The percentof excess aluminum for the aluminum reaction amounted to 33%.

The foregoing example demonstrates the large-scale commercialfeasibility of this process wherein phenol-free thiophenol of 99.1%purity was obtained in a yield of 96.3%. The use of aluminum metal toremove tar acids from tar acid-contaminated thiophenols is hence ofconsiderable commercial interest.

Although it is generally preferred for the purposes of this invention touse aluminum that has not been treated with mercury, for certainspecific purposes mercurated aluminum may be used, i.e., a preformedaluminum amalgam or an aluminum-mercury complex formed in situ by theaddition of aluminum and a mercury salt. A preferred mercurated aluminumreactant for use in the present invention is aluminum together with aminor quantity of mercuric chloride. Other inorganic mercuric salts arealso suitable for use with the aluminum, such as the bromide, nitrate,cyanide, or the like, which salts are readily available. In general, forin situ amalgamation, any mercury salt somewhat soluble in thethiophenol being treated is considered suitable. The mercuric halides,specifically mercuric chloride, are particularly preferred'because oftheir efiectiveness and ready availability. It is believed that actualamalgamation of the aluminum occurs in situ. However, the exactcomposition of the amalgam or complex formed is not known.

An active aluminum amalgam may be prepared by contacting granularaluminum (2030 mesh) with a saturated ethereal solution of mercuricchloride for 0.5 minute at the boiling point of the solution. Thesupernatant liquor is then quickly decanted, and the aluminum is washedby decantation with two portions of dry ether. The amalgamated aluminumshould be prepared just prior to use. Other methods of preparing apreformed aluminum amalgam are also suitable.

During the course of the reaction the amalgam or the mercury salt used,such as mercuric chloride, is converted to mercury metal. The mercury isgenerally recovered in a finely divided colloidal state. Depending onthe type of equipment employed, greater or less amounts of the mercurywill be recovered with the thiophenol distillate. Thus where previouslyfractionated contaminated thiophenol was treated with mercuric chlorideand aluminum at its atmospheric reflux temperature and the pressure wasthen reduced, it was found that the phenol-free thiophenol recovered byrapid distillation through a Vigreaux column contained mercury. Only theinitial drops of distillate were cloudy due to the presence of finelydivided mercury. The mercury appeared to have been transportedmechanically up the walls of the column by the rising ring ofcondensate. The remainder of the distillate was clear. It has also beenobserved that where a packed column is used in place of a Vigreauxcolumn, most of the distillate fractions will contain mercury metal.Apparently because of the fine state of subdivision of the mercury, itspresence in the overhead distillate appears indigenous to the variousprocedures used. However, the amount present will depend on the type ofequipment employed. Also, after a short period of storage the colloidalmercury will tend to coagulate and hence be more readily separated fromthe distillate which then may be obtained essentially free of mercury.

In general, the use of mercurated aluminum introduces problems of columncleanup and distillate contamination. Further, for most commercialapplications removal of the mercury is a desideratum. The mercury may beremoved by concentrating it in the early distillate fraction; settlingand centrifugation techniques are also feasible.

Where a greater than a stoichiometric amount of mercurated aluminum isused in the reaction, after the tar acids have been converted to thecorresponding aluminum phenoxides, and traces of water and alcohols havebeen reacted with, in the presence of mercury salt the excess aluminumwill react at substantially the same reaction temperature with thethiophenols present. It has been observed that where mixed thiocresolsare present, in the presence of the mercury salt the excess aluminum, inan amount sufficient to combine with only a portion of the thiocresols,selectively reacts with the metaand para-thiocresols present so as toenrich the o-thiocresol content of the mixture. Thus mercurated aluminumfinds further applicability for concentrating a mixture of thiocresolswith respect to its o-thiocresol content.

The following examples illustrate the use of mercurated aluminum in thisinvention but are not intended as limitations thereof.

EXAMPLE 7 Reaction 0 aluminum-mercury salt with syntheticthiophenol-phenol mixture A synthetic sample of commercially availablereagentgrade phenol and 99+ percent thiophenol was prepared. Thiscomposite synthetic sample contained 97.5 percent thiophenol and 2.5percent phenol. Of the mixture, 350 grams (0.093 mole phenol) wastreated with 1.80 grams aluminum (0.067 gram atoms aluminum) and 1.05grams of mercuric chloride. This corresponded to 0.51 weight percentaluminum based on the feed. The temperature was raised to 169 C. and avigorous reaction ensued during which hydrogen gas was generated andvented. The thiophenol was then distilled off at reduced pressure andthe product was analyzed by vapor-phase chromatography. Ninety-fourweight percent recovery of thiophenol free from any phenol was obtained.No phenol could be detected in the chromatogram.

EXAMPLE 8 Reaction of aluminum-mercury salt with petroleum dis tzllatefraction containing thiophenol and phenol '9 EXAMPLE '9 A sampleobtained from the naphtha fraction of a petroleum distillate was foundto contain 972 percent mixed thiocresols and 2.8 percent ofcreso'l.Upon-treatment with 0.72 weight percent aluminum and 0.3 percentmercuric chloride, based on feed, following the procedure as set forthin Example 8, 91 weight percent of thio'cresols free from tar acid wasobtained. No tar acids could be detected by vapor :phase chromatography.

EXAMPLE Reaction of aluminum-mercury salt'with petroleum distillatefraction containing thiocresols and cresols An excess of aluminum wasused to treat a 435-gram sample containing 94.5 percent mixedthiocresols. Analysis of the sample showed the following to be present:

o-thiocresol34.4 percent (36.4 percent of mixed thiocresol-s)m-thiocresol-45.1 percent (47.7 percent of mixed thiocrcsols)p-thi-ocresol-15.0 percent (15.9 percent of mixed thiocresols)o-cresol2.2 percent m-p-cresol-3.3 percent The mixed thiocresol andcresol content was determined by vapor-phase chromatography. Thespecific distribution of isomers was found by infraredspectrophotometry. Fifteen grams of aluminum was used, corresponding to3.4 weight percent aluminum based on the total feed; 2.5 grams HgCl wasadded. The aluminum was added in several portions to control thereaction. Thi batchwise addition is preferred where relatively largeproportions of aluminum are used, as in this example. Followingdistillation, 54 weight percent of thiocresols free from tar acids wasrecovered. Analysis of the distillate by vapor-phase chromatography andinfrared spectrophotometry showed 50.8 percent o-thiocresol, 36.8percent m-thiocresol, and 12.4 percent p-thiocresol. No tar acids couldbe detected.

As shown in this example, the aluminum selectively reacts with themetaand para-thiocresol-s, since these are diminished relative to theortho-isomer in the recovered thiocresols.

EXAMPLE 11 Reaction of aluminum-mercury salt with petroleum distillatefraction containing thiocresols and o-cresol A sample containing 97.2percent mixed thiocresols and 2.8 o-cresol was treated with mercuricchloride and 3.4 weight percent aluminum, as described for Example 10.No tar acids could be detected in the thiocreso-l product. Thethiocresols originally present were o-thiocresol 32.1 percent,m-thiocresol 51.9 percent, and p-thiocresol 13.2 percent (97.2 percent).The analysis of the recovered product showed o-thi'ocresol 43.2 percent,m-thiocresol 44.0 percent, and p-thiocresol 12.8 percent (100 percent).

EXAMPLE 12 Reaction of aluminum-mercury salt withthiophenolphenol-neutral oil mixture Thiophenol, 750.4 grams, containing3.2 weight percent phenol and 0.7 weight percent neutral oil (non-acidichydrocarbons) as obtained from a petroleum distillate fraction wasreacted with 27 gram of granular aluminum in the presence of 3.3 gramsof mercuric chloride as in previous examples. Distillation at 50 mm. Hgpressure yielded 270 grams of phenol-free thiophenol oontaining 1.2weight percent neutral oil.

. 10 t EXAMPLE '13 Attempted reaction of magnesium-mercuric :chloridewith thiophenol-phenol mixture -A mixture consisting of 377.7 grams ofthiophenol and 5.4 grams of phenol was heated to 168 C. with 2.00 gramsof magnesium turnings. No gas evolution occurred.

Then 1.2 grams'of HgCl was added and the temperature wa maintained at"C. for 22 minutesstill no gas evolution. Finally, 1.00 gram of granularaluminum (2030 mesh) was added. Reaction occurred within 13 minutes. oncompletion of the Vigorous reaction, the supernatant liquor was decantedand, after washing with toluene and petroleum ether, 2.6 grams ofunreacted magnesium and mercury metals were recovered. 'No aluminumremained unreacted.

Despite the less acid nature of phenols compared with thiophenols,aluminum phenoxides are ordinarily formed with greater ease and at lowertemperatures than the corresponding aluminum thiophenoxide's. However,when all the phenols present are combined with aluminum, the presence ofa mercury salt allows the further rapid reaction of aluminum with thethiophenols to form an aluminum thiophenoxide. This is of particularutility Where it is desired to selectively concentrate a mixtureconsisting only of mixed thiophenols. Also, where the phenol isrelatively low-boiling, the presence of a mercury salt activates thealuminum metal so that the phenoxide reaction may take place at a lowertemperature at atmospheric pressure, which might otherwise not befeasible.

The formation of the aluminum phenoxide has been found to proceedsatisfactorily at atmospheric pressure when a preformed aluminum amalgamis used. The use of the preformed amalgam may be preferred whererelatively low reaction temperatures are desired. However, where it isdesired to use mercurated aluminum, it is generally preferable and moreconvenient to activate the aluminum metal in situ by adding it to thethiophenolphenol mixture together with a suitable mercury salt, such asmercuric chloride, cyanide, bromide or the like.

The mechanism that occurs in the reactions of thi in vention isconsidered a highly complex one. While it is not desired to have thescope of this invention restricted by any explanation profiered, it isconsidered apparent that the formation of aluminum phenoxide proceeds ata very much more rapid rate than that of aluminum thiophenoxide. Henceunder the conditions used, the reaction is highly selective. Thisselectivity phenomenon occurs despite the fact that thiophenol is aconsiderably stronger acid than phenol, and hence the thiophenol mightordinarily be expected to be more reactive than the phenol. However, asis shown herein, not only is the selective reaction with phenol favored,but apparently the aluminum will react with the phenol to the completeexclusion of the thiophenol as long as any phenol is present.

While this invention has been described with respect to specificpreferred embodiments, it is not desired to be limited by theillustrative examples given or by the speculative mechanisms postulatedfor this reaction. The scope thereof should be determined in accordancewith the objects and claims herein set forth.

We claim:

1. The process for purifying a tar acid-contaminated thiophenol whichcomprises reacting a mixture containing a thiophenol and a tar acid withaluminum to selectively form an aluminum salt of the .tar acid, andseparating the thiophenol from said salt.

2. The process for recovering a thiophenol in substantially pure formfrom a mixture containing a thiophenol and a tar acid which comprisesadding to said mixture aluminum in an amount sufiicient to provide atleast /3 gram atom of aluminum per mole of tar acid present to reactselectively with the tar acid to form an aluminum 11 salt thereof, anddistilling ofi the thiophenol substantially free from tar acid.

3. The process for recovering a thiophenol in substantially pure formfrom a mixture containing a major portion of a thiophenol and a minorportion of a tar acid which comprises adding at least /3 gram atom ofaluminum per mole of tar acid present to said mixture, heating saidmixture to a temperature between 100 and 220 C. at which a reactionoccurs and hydrogen is evolved, continuing said heating until evolutionof said hydrogen has substantially ceased, and distilling off athiophenol from the mixture in substantially pure form free from taracid.

4. The process according to claim 3 wherein said thiophenol is athiocresol and said tar acid includes a cresol.

5. The process according to claim 3 wherein said thiophenol is athioxylenol and said tar acid includes a xylenol.

6. The process according to claim 3 wherein the aluminum consists offinely divided aluminum foil having a purity of at least 99 percent byweight.

7. The process for recovering thiophenol per se in substantially pureform from a mixture containing a major portion of thiophenol and a minorportion of phenol which comprises adding at least /3 gram atom ofaluminum per mole of phenol present to said mixture, heating saidmixture to a temperature between 135 and 165 C. at which a reactionoccurs and hydrogen is evolved, continuing said heating until evolutionof hydrogen has substantially ceased, and distilling off the thiophenolfrom the mixture in substantially pure form free from phenol.

No references cited.

1. THE PROCESS FOR PURIFYING A TAR ACID-CONTAMINATED THIOPHENOL WHICHCOMPRISES REACTING A MIXTURE CONTAINING A THIOPHENOL AND A TAR ACID WITHALUMINUM TO SELECTIVELY FORM AN ALUMINUM SALT OF A TAR ACID, ANDSEPARATING THE THIOPHENOL FROM SAID SALT.